Apollo 10: The Dress Rehearsal

On 18 May 1969, a king,* some
congressmen, other distinguished guests, and a hundred thousand other
watchers waited at scattered vantage points around the Cape area. At 49
minutes past noon, Rocco Petrone's launch team sent Apollo
10 on its way to America's second manned rendezvous with the
moon. Humming along at first like a Titan II, or so its
Gemini-experienced crewmen felt, the gigantic Saturn V first stage
suddenly slammed Stafford, Cernan, and Young forward and backward, until
the cabin dials blurred before their eyes. Stafford tried to tell chief
Flight Director Glynn Lunney's mission control team when the first stage
of the vehicle dropped off but he could not squeeze the words out. When
the remainder of the stack steadied, the S-II second stage (already
firing) had the same pogo tendencies. The three astronauts had begun to
wonder if the vehicles would hold together, especially the lunar module
below them, when the S-IVB third stage fired, growling, rumbling, and
vibrating as it shot into earth orbit.43

In the launch control room 18 May 1969, Apollo officials (standing
left to right) George Low, Samuel Phillips, Donald Slayton, and (seated
left to right) John Williams, Walter Kapryan, and Kurt Debus listen to
the countdown for the launch that would send three astronauts toward the
moon.

During the systems review period, the ride smoothed. Lunney checked the
men at the monitors in the control room and they all voted to fire for
translunar injection. Stafford's crewmen considered not wearing their
helmets and gloves but "chickened out," as Young phrased it,
and put them on. They probably found the extra garb comforting when the
S-IVB fired, because the third stage again groaned and shook. None of
the three were confident of being able to continue the trip much longer,
and Cernan wondered how the mission could be safely aborted at this
point in space. The guidance system kept Apollo 10 on a
steady course, however, and they were on their way.44

When Young pulled the command module away from the S-IVB, the crew saw
the panels that had housed the lunar module drift away. After the
command module was flipped around, it was 45 meters away from the third
stage, about three times farther than intended, but it would take only a
little extra gas to get back for docking. As the CM moved around, the
mission controllers on the ground watched the maneuvers, in "living
color."

At 66,600 kilometers outward bound, the crew televised a
near-circular view of the earth to Mission Control and the
public.

Television had worked so well on other Apollo flights that NASA had
decided to put a color system on Stafford's command module. Weighing
only 5.5 kilograms, the Westinghouse camera included a 7.5-centimeter
monitor to show the astronauts what they were transmitting. Now flight
controllers watched along with the crew as Charlie Brown,
perfectly aligned with his target, pulled up to Snoopy,
latched onto him, and drew him out of his doghouse. Shortly thereafter,
with signals to Houston through the big antenna dish at Goldstone,
California, a vast populace saw a color view of a large portion of their
western hemisphere from thousands of kilometers in space.45

They also photographed the view, showing much of the North
American continent.

After checking tunnel, latches, and docking probe, the crewmen had a
light workload as they coasted toward the moon. They were grateful for
even such small jobs as firing the thrusters to make slight corrections
in spacecraft attitude, but this was so seldom necessary they began to
wonder if the jets were working. On occasion, however, when nothing was
firing, the whole stack shimmied. They later speculated that this may
have been caused by fuel sloshing. When making optical navigational
sightings, the crew had trouble acquiring enough stars for an accurate
reading. Without the optics, the men could see no stars at all for a
long time. Finally, Stafford spotted a few dim orbs after he had
traveled 190,000 kilometers into space. But not much navigating was
needed; the course was so true that the service module propulsion system
was used only once, to add 15 meters per second to their speed, at 26
hours into the voyage. This firing put the spacecraft on a lunar path
that would lead the crew over the exact spot where the first landing
might be made. The rest of the time the astronauts studied the flight
plan, slept, ate, and beamed five excellent television transmissions
back to the earth.46

Stafford, Cernan, and Young were the first Apollo pilots to be free from
illness during the mission, although Cernan experienced a slight
vestibular disturbance. Like all their colleagues who had flown before,
once they unbuckled from the couches they had a stuffy feeling in their
heads. This lasted for 8 to 10 hours for Stafford and Young; Cernan
gradually lost the sensation over the next two days. He practiced
"cardinal head movements" that the medics thought might help
overcome his slight feeling of nausea. Although he was able to do the
exercise for more than four minutes at a session by the seventh day of
flight, when he returned to earth he lambasted the procedure, saying it
must have been designed to bring on illness rather than to alleviate
it.47

The crew slept well, although thruster firing bothered Cernan the first
night. Later, when they were circling the moon, the men were glad that
McDivitt's crew had suggested they carry a sleeping bag apiece. The
spacecraft grew cold once the windows had been covered to darken the
cabin for sleeping.

One major complaint the astronauts registered was about their water
supply. They were supposed to chlorinate it at night; because of an
error in procedures passed to them by flight control, Stafford had a
double dose of chlorine when he took a drink during the first breakfast
of the trip. This was unpleasant, but it posed no major problem.
Something else in the water supply did. When earlier crews had
complained about gas in the water system, a new water bag was designed,
with a handle the crew could use to whirl the bag around to separate the
gas from the water. It did not work. The gas settled to the bottom of
the bag and then remixed with the water when the crew members tried to
drink. The gas worried them; they could envision getting diarrhea, which
would have been difficult to cope with during flight. They did have gas
pains and cramps but, fortunately, nothing more.48

Poor water quality may have affected their appetites, for the astronauts
on this flight were not big eaters. On occasion, they skipped meals.
Stafford estimated they had enough food to last for 30 days. Not all the
blame could be laid on the water, however; the food was still no
epicurean delight. Back on earth in early May, Donald D. Arabian, chief
of the Apollo Test Division, had tried a four-day supply of their
rations. Arabian claimed to be "somewhat of a human garbage
can," but even he lost his desire for food on this diet. The
sausage patties, for example, tasted like granulated rubber and left an
unpleasant taste. With all the difficulties of preparation, Arabian
added, by the third day continuing the test was a chore. He did like the
items that were closest to normal table foods. Stafford's crew also
found some of the newer dishes that could be eaten with a spoon quite
palatable. But the men dreaded reconstituting the dehydrated meals,
knowing that the water contained so much gas.49

Unlike Borman's crew, which could not see the moon with the unaided eye
until the spacecraft was almost upon it, Stafford's group spotted it on
the second day of flight. On the earth, it looked like a waxing
crescent, but Stafford and Young, with the help of earthshine, could see
almost a full moon. Although the moon was much bigger at 200,000
kilometers above the earth, landmarks on the lunar surface still could
not be picked out. Cernan also asked flight controllers if they thought
he could really recognize the S-IVB stage 5,600 kilometers away, because
that was what he thought he was seeing. The CapCom told him that the men
in the control room were nodding their heads yes and that the distance
between the two vehicles actually measured 7,400 kilometers.50

When Apollo 10 reached the lunar vicinity on 21 May, the
controllers informed the crewmen that at one time or another more than a
billion persons had watched their televised activities. But interest now
focused on the exact moment when their craft would shoot around the moon
and lose communications with the earth. At 74 hours 45 minutes into the
mission, flight control predicted that loss of signal would come at 75
hours, 48 minutes, 24 seconds. The controllers had already determined
that the ship would reach the moon 11 minutes later than scheduled,
since there had been only one midcourse correction, rather than two. Its
trajectory would be 110 kilometers above the lunar surface.51

The crew was impressed by the lunar landscape, although Stafford
insisted it looked like a big plaster of Paris cast. The three found it
almost incredible that someone back on earth had been smart enough to
place them within 110 kilometers of the moon - but there they were. They
caught just a glimpse of the surface a minute before they fired the
service module engine to go into lunar orbit, an activity that required
all their attention. The six-minute retrograde maneuver seemed
interminable, just as it had to Borman's group, but the engine kept
firing and their confidence in it kept growing. When the engine finally
shut down and they were sure that it had done its job, Stafford and
Cernan had time to look at the lunar surface. They likened one area to a
volcanic site in Arizona. Finally Stafford forced his attention back
inside the cabin and told his crewmates that he thought the best thing
to say when they got back in radio contact was, "Houston, tell the
earth we have arrived."52

Site 3 was on the lunar equator, in Central Bay; topographic
features are accentuated by the low-sun angle.

Stafford, Young, and Cernan were fascinated by how much more slowly they
seemed to travel around the moon than they had around the earth. They
liked the slower pace, because on the first circuit they would pass
directly over the area where Apollo 11 was due to land two months later.
They had barely rounded the corner before Stafford and Cernan began
describing the physical features down the highway they called "U.S.
1," leading to the landing site. By the third circuit, the world
was sharing the view on color television. Watchers could see the gray,
white, black, and brownish tints of the landing site, which seemed to be
free from boulders, providing a smooth landing field.53

Six hours after reaching the moon, Cernan and Stafford began getting the
lander ready. The hatches, probe, and drogue were easily removed. As he
entered the lunar module, Cernan was greeted by a snowstorm of mylar
insulation, apparently sucked into the vehicle through a vent from the
tunnel. The insulating material had come loose in the tunnel, and the
crewmen had spent some time capturing and cleaning it up in the command
module. Now they had the same job to do in the lunar module.

Cernan had floated head down through the tunnel into the lunar module.
Because the two spacecraft were locked together from top to top, his own
private world had a new orientation. He later commented that the best
way to handle this psychologically was to slide through the hatch, look
around, and then mentally assign an arbitrary up and down. Once he had
accepted the new environment, he had no problems in checking, hauling in
equipment, and getting things in order. The crew had intended to leave
the passageway to the lander open after returning to the command ship,
but the hardware was too bulky. It was simpler, and quite easy, to put
the probe and drogue back into place.54

Flight control had planned to let the crew sleep until the last moment
on 22 May, when Stafford and Cernan would leave Young and fly the lander
down near the lunar surface. But, after playing "The Best Is Yet to
Come" and sounding reveille, ground control found that the
astronauts had stealthily risen, eaten breakfast, and quietly begun work
on the flight plan checklist. Cernan removed the encumbrances from the
tunnel and zipped over into the lunar module to get everything ready,
while Young helped Stafford with his suit (a five-minute job even with
assistance).** Cernan then came
floating back into the command module and jumped into his suit. When
flight control heard from them at the start of the tenth circuit, the
two pilots were in the lander and closing off the tunnel.55

When Stafford and Cernan were ready for undocking, however, they found
that the lunar module had slipped three and a half degrees out of line
with the command module at the latching point, possibly because of loose
mylar collecting on the docking ring. It might also have happened when
Young, during docking, had forgotten to turn off the service module roll
thrusters and flight control had been tardy in reminding him of the
task. Whatever caused the problem, the crew feared separating the two
craft might shear off some of the latching pins, possibly preventing
redocking. Stafford and Cernan would be stranded in lunar orbit with no
way back except by going out the lander hatch and making their way to
the command module hatch - a dangerous undertaking. But Low, who was in
the control room at the time, told Flight Director Lunney that as long
as the misalignment was less than six degrees they could go ahead and
undock.56

Just before Apollo 10 rounded the corner to the back of the
moon, flight control passed the good news to Stafford. The two crewmen
in LM Snoopy heard a "pow" as they broke free.
Young, all alone in what now seemed to be an unusually large command
module, turned on the television camera so the flight controllers back
on the earth could help him inspect the lander. Meanwhile the lunar
module landing gear had deployed and was in place. The lander's systems
checked out well, especially the radar, the abort guidance system, the
antennas, and the pressurization of the descent propulsion system.
Everything looked good, and everybody was ready to go. Telling Young not
to get too lonesome and not to go off and leave them, Stafford and
Cernan announced that they were ready to go down and snoop around the
moon.57

Young had used his service module thrusters to pull Charlie
Brown nine meters away from the lunar module for the inspection.
He then gave the same jets a spurt to thrust downward toward the moon
until the two vehicles were three and a half kilometers apart. Stafford
and Cernan were ready to try, for the first time, another of the
operations with a significant Apollo abbreviation so cherished by the
engineers - descent orbit insertion, or DOI. At nearly 100 hours into
the mission, Stafford started the descent engine at minimum thrust -
which slowly built up past 10 percent - and then 15 seconds later he
increased it to 40 percent for 12 more seconds. The engine ran smoothly,
with none of the chugging experienced on McDivitt's ride. Young tracked
the burn optically and told the lunar module crewmen that they were
moving away from him at more than 20 meters a second. Cernan did not
think they were going that fast. "It's a very nice pleasant
pace," he said. Now they could get a close look at a proposed
landing site in the Sea of Tranquility, where Apollo 11 might set down
in July.58
Stafford and Cernan had studied hard for what they were going to do. In
a T-38 aircraft, they had simulated this trajectory above the earth.
They had pored over charts and maps of the site, and they had
scrutinized the area during their hours in lunar orbit. So the
astronauts traveled easily down the approach path, calling out the names
of craters, rilles, and ridges as they went along. They appeared to be
traveling exactly over the track they wanted, reaching a low point of
14,447 meters above the surface. They took many pictures; then
Stafford's camera failed as the film started to bind. He described the
landing site as much like "the desert in California around
Blythe." If a lander touched down on the near end, it would have a
smooth landing, he said; but, if it wound up at the far end of the zone,
extra fuel would be needed for maneuvering to a clear spot. Their
landing radar worked perfectly when they tested it, and the pilots
remarked that they had no visibility problems with lighting and sun
angles.59

Young caught sight of the lunar module at a distance of 120 kilometers;
Snoopy appeared to be running across the lunar surface like
a spider. At other times, using a sextant, he spotted the craft as far
away as 550 kilometers. An hour after the first descent burn, Stafford
and Cernan fired the engine again, to shape the trajectory for their
return to the command module. Shoving the throttle forward for 40
seconds and 100 percent thrust, Stafford was happy to note that there
was still no chugging. Young tried to see the flames from the engine but
could not. Although the lander's speed had increased by 54 meters per
second, the crew again had the impression that acceleration was slow.
During these activities, the lunar module had a "hot [open]
mike," which was fine with Young, since it kept him informed of
what was happening in the lander. But whenever he talked, he had a
feedback of his own voice. Somebody would have to fix that before the
next mission, he said.60

After Stafford's camera failed, he and Cernan had little to do except
look at the scenery until time to dump the descent stage. Stafford had
the vehicle in the right attitude 10 minutes early. Cernan asked,
"You ready?" Then he suddenly exclaimed, "Son of a
bitch!" Snoopy seemed to be throwing a fit, lurching
wildly about. He later said it was like flying an Immelmann turn in an
aircraft, a combination of pitch and yaw. Stafford yelled that they were
in gimbal lock - that the engine had swiveled over to a stop and stuck -
and they almost were. He called out for Cernan to thrust forward.
Stafford then hit the switch to get rid of the descent stage and
realized they were 30 degrees off from their previous attitude. The
lunar module continued its crazy gyrations across the lunar sky, and a
warning light indicated that the inertial measuring unit really was
about to reach its limits and go into gimbal lock. Stafford then took
over in manual control, made a big pitch maneuver, and started working
the attitude control switches. Snoopy finally calmed
down.61

For this first lunar module flight to the vicinity of the moon, the
pilots were supposed to use the abort guidance system instead of the
primary guidance system, to test performance in the lunar environment.
The abort system had two basic control modes, "attitude hold"
and "automatic." In automatic, the computer would take over
the guidance and start looking for the command module, which was
certainly not what the crew wanted to do just then. In correcting for a
minor yaw-rate-gyro disturbance, the pilots had accidentally switched
the spacecraft to the automatic mode, and the frantic gyrations
resulted. From Cernan's startled ejaculation to Stafford's report that
everything was under control took only three minutes. Flight control
told the crewmen they had made an error in switching, but the system was
fine. They could fire the ascent engine. After the firing, the lander
flew what Stafford called a "Dutch roll," yawing and pitching
and snaking along. When the engine shut down, however, to the crew's
surprise the attitude and flight path to the command module were
correct. From a maximum distance of 630 kilometers, the thrust from the
ascent engine moved the lunar module to within 78 kilometers of the
mother ship.62

Young, by himself in CM Charlie Brown, said that LM
Snoopy carrying Stafford and Cernan close to the moon below
looked like a spider crawling on the lunar surface. Young photographed
the returning lunar module, which successfully demonstrated the
lunar-orbit rendezvous operations.

As the lunar module approached, Young saw it through his sextant at a
distance of 259 kilometers. Stafford and Cernan got a radar lock on the
command module shortly after the insertion burn and watched with
interest as the instrument measured the dwindling gap between the
vehicles and demonstrated the theories of orbital mechanics in actual
practice. Cernan especially liked the steady communications that kept
both crews aware of what was happening. After watching the command
module from as far away as 167 kilometers and then losing sight of it at
sunset, the lunar module pilots saw Charlie Brown's
flashing light with their unaided eyes at 78 kilometers. At last, the
two craft were only eight meters apart, and the relative speed between
them was zero. Stafford did find the ascent stage a little difficult to
hold steady, just as Conrad had suspected, but Young slid the probe
smoothly into the dead center of the drogue. Stafford rammed the lunar
module forward, and the capture latches closed with a loud bang.63

Stafford and Cernan had been gone for more than eight hours, and they
were ready to get back into the command module and rest. Transfer ring
equipment and closing the tunnel were easy. When all three were settled
in, they cut the lander loose. Flight control then fired the ascent
engine to fuel depletion (249 seconds) and sent the lunar module into
solar orbit. The crew watched it move away; Snoopy was soon
out of sight. Stafford and his crew went back to tracking landmarks on
the surface below for the upcoming lunar landing mission.64

After 31 circuits, the crew fired the service module engine to begin the
return to the earth. On 26 May 1969, Apollo 10 streaked
through the early morning darkness like a shooting star, to splash down
in the Pacific 690 kilometers from Samoa and only 6 kilometers from the
prime recovery ship. The journey had taken 192 hours, 3 minutes, 23
seconds. A helicopter picked the crew up and carried them to the U.S.S.
Princeton within the hour. This fantastic voyage was over
and had revealed absolutely no reason why Apollo 11 could not negotiate
the final few kilometers to the lunar surface. The trail had been
blazed.65

Apollo 10 crewmen Stafford, Young, and Cernan (left to right) meet
the press at Manned Spacecraft Center on 7 June 1969 after return from
their lunar-orbit mission.

* King Baudoin and Queen Fabiola of
the Belgians flew to KSC on Air Force One two hours before
liftoff.

** Getting into and out of the suits
in the small lunar module would be difficult, the crewmen realized,
although they found that putting them on was not too great a chore.
Simpler procedures would have to be worked out for crews that would
remain in the lander for longer periods.